Phentolamine Mesylate

Contraindications

• MI or history of MI.177 a However, results of some studies indicate that the drug may have a beneficial effect in patients with MI.a

• Coronary insufficiency, angina, or other evidence suggestive of CAD.177 a

• Known hypersensitivity to phentolamine, related compounds, or any ingredient in the formulation.177 a

Warnings/Precautions

Warnings

Risk of MI, cerebrovascular spasm or occlusion, usually in association with marked hypotension.177 a

Risk of tachycardia, cardiac arrhythmias; defer cardiac glycoside administration until cardiac rhythm returns to normal.177

Risk of severe hypotension or other signs and symptoms of shock; treat with prompt supportive measures and norepinephrine (if necessary).a Do not administer epinephrine for hypotension since it may cause a paradoxical fall in BP.a

Phentolamine and other pharmaceutical tests no longer procedures of choice for diagnosis of pheochromocytoma; may be used when additional confirmatory evidence of pheochromocytoma is required and the potential benefits of the tests outweigh the possible risks.177 a Urinary assay of catecholamines or other biochemical assays are the safest and most reliable methods.177 a Consider that no test is completely reliable.177 a

Possible false-negative responses to phentolamine test (e.g., in patients with paroxysmal hypertension or with a pheochromocytoma not secreting enough epinephrine or norepinephrine to elevate BP or sustain an elevation).a

False-positive reactions (occurring more commonly than false-negative) reported in patients with essential hypertension, uremia, or in those who received sedatives, opiates, or antihypertensive drugs.a (See Specific Drugs under Interactions.)

Do not perform test on normotensive patients.a

Major Toxicities

Intracavernosal therapy for impotence could result in persistent priapism (a medical emergency) which requires immediate medical and/or surgical intervention.103 105 106 107 108 110 113 115 116 120 124 125 126 127 128 If not treated immediately, penile tissue damage and permanent loss of potency may occur.142 152 161 162 163

Intracavernosal therapy (administered by self-injection) may be problematic in patients receiving anticoagulants, those who cannot tolerate transient hypotension, and those with poor manual dexterity, poor vision, or severe psychiatric disease.125

General Precautions

Use with caution in patients with gastritis or peptic ulcer.a

Monitor left ventricular function and ECG continuously during IV infusion of the drug.a

Specific Populations

Category C.177

Not known whether phentolamine is distributed into milk.177 Discontinue nursing or the drug.177

Common Adverse Effects

Abdominal pain, nausea, vomiting, diarrhea, exacerbation of peptic ulcer, weakness, dizziness, flushing, orthostatic hypotension, and nasal congestion.177 a

Storage

Parenteral

15–30°C.177 a

Use reconstituted solution at time of preparation; do not store.177 a

Compatibility

For information on systemic interactions resulting from concomitant use, see Interactions.

Drug Compatibility

• Competitively blocks α-adrenergic receptors (primarily excitatory responses of smooth muscle and exocrine glands), but action is transient and incomplete.a

• More effective in antagonizing responses to circulating epinephrine and/or norepinephrine than in antagonizing responses to mediator released at the adrenergic nerve ending.a

• Causes peripheral vasodilation and decreases peripheral resistance, primarily by direct relaxation of vascular smooth muscle, but α-adrenergic blockade also contributes to vasodilation.a

• Stimulates β-adrenergic receptors and produces a positive inotropic and chronotropic effect on the cardiac muscle (increasing cardiac output)a and vascular effects on vascular smooth muscle.177

• Usual doses lower BP maintained by circulating epinephrine or norepinephrine, but have little effect on the BP of healthy individuals or patients with essential hypertension.a

• In patients with AMI associated with hypertension and/or left ventricular failure, administration of IV phentolamine results in improvement in left ventricular performance; cardiac output, stroke index, heart rate, and cardiac index are increased and left ventricular filling pressure is decreased.a

• Advise patients (using intracavernosal therapy for impotence) to contact their clinician if they develop a persistent (e.g., longer than 4 hours) erection during such therapy.132 133

• Importance of informing clinicians of existing or contemplated therapy, including prescription and OTC drugs and dietary or herbal supplements, as well as any concomitant illnesses.

• Importance of women informing their clinician if they are or plan to become pregnant or plan to breast-feed.177 a

• Importance of informing patients of other important precautionary information. (See Cautions.)